LED backlight unit without printed circuit board and method of manufacturing the same

ABSTRACT

Disclosed herein is a Light Emitting Diode (LED) backlight unit without a Printed Circuit board (PCB). The LED backlight unit includes a chassis, insulating resin layer, and one or more light source modules. The insulating resin layer is formed on the chassis. The circuit patterns are formed on the insulating resin layer. The light source modules are mounted on the insulating resin layer and are electrically connected to the circuit patterns. The insulating resin layer has a thickness of 200 μm or less, and is formed by laminating solid film insulating resin on the chassis or by applying liquid insulating resin to the chassis using a molding method employing spin coating or blade coating. Furthermore, the circuit patterns are formed by filling the engraved circuit patterns of the insulating resin layer with metal material.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2006-0025803, filed on Mar. 21, 2006, entitled “Light EmittingDiodes-Backlight Unit without printed circuit boards and Manufacturingmethod thereof”, which is hereby incorporated by reference in itsentirety into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a backlight unit installed ina Liquid Crystal Display (LCD) device and, more particularly, to a LightEmitting Diode (LED) backlight unit without a Printed Circuit board(PCB), in which light source modules, that is, LED packages, aredirectly mounted on a chassis.

2. Description of the Related Art

A backlight unit is a device that is installed in an LCD using theprinciple in which liquid crystals change their molecular arrangementaccording to applied voltage, and provides light and illuminates ascreen from behind. Although backlight units to which one or morecold-cathode tubes are applied were mainly used, backlight units towhich LEDs are applied currently attracts attention due to theiradvantages with respect to life span, brightness, color reproducibility,etc.

Unlike cold-cathode tubes, LEDs require substrates when they are used aslight sources. Since such LEDs emit large quantities of heat whileradiating light, metal core substrates (metal core printed circuitboards), having an excellent heat dissipation characteristic, have beenused.

Although metal core substrates have an excellent heat dissipationcharacteristic, they are very expensive. Accordingly, the high cost ofthe metal core substrates is one of the principal factors that decreasethe cost competitiveness of the backlight units formed of the metal coresubstrates. As a result, there is a trend toward the use of relativelyinexpensive epoxy resin insulating substrates. An example of aconventional backlight unit in which LEDs are mounted on such aninsulating substrate is illustrated in FIG. 4.

As illustrated in FIG. 4, a backlight unit 200 includes an insulatingsubstrate 210, a plurality of LED packages 230, and a chassis 250.

Circuit patterns 211 and 212 are formed on the insulating substrate 210by coating an epoxy resin FR4-core with a copper foil and etching thecopper foil.

Each of the LED packages 230 is mounted such that an LED chip 231 isdirectly connected to one LED electrode 232 and is wire-bonded to theother LED electrode 233.

The LED chip 231 and the LED electrodes 232 and 233 are placed within aplastic mold casing 234, and the casing 234 is covered with an epoxyresin lens 235.

The LED package 230 is mounted on the insulating substrate 210, and iselectrically connected to positive and negative electrodes, that is, tothe circuit patterns 211 and 212.

The chassis 250 is made of material having excellent thermalconductivity, such as metal, and is placed beneath the insulatingsubstrate 210, and a heating pad 270 is placed therebetween so as toprovide electrical insulation and decrease contact thermal resistance.

In the conventional backlight unit 200 having the above construction,when the total thermal resistance is calculated, with the assumptionthat the thickness t_(substrate) of the substrate 210 is 0.8 mm, thethermal conductivity K_(substrate) of the substrate 210 is 0.35 W/m° C.,the thickness t_(heating pad) of the heating pad 270 is 0.2 mm, thethermal conductivity K_(heating pad) of the heating pad is 1.00 W/m° C.,and the area A of the substrate 210 or the heating pad 270 is 36 mm²,

$\begin{matrix}{R_{total} = {R_{substrate} + R_{{heating}\mspace{11mu} {pad}}}} \\{= {\left( {{t_{substrate}/K_{substrate}} + {t_{{heating}\mspace{11mu} {pad}}/K_{{heating}\mspace{11mu} {pad}}}} \right)/A}} \\{= {\left( {{0.8*{10^{- 3}/0.35}} + {0.2*{10^{- 3}/1.00}}} \right)/\left( {36*10^{- 6}} \right)}} \\{= {69.4{^\circ}\mspace{11mu} {C.\text{/}}W}}\end{matrix}$

As explained above, the total thermal resistance is very high. When thethickness of the heating pad 270 is 0.5 mm, a total thermal resistanceof 77.88° C./W results.

As a result, the insulating substrate of the conventional backlight unithaving the above-described construction exhibits very poor thermalconductivity, therefore it is difficult to effectively eliminate heatgenerated by the LED chips, with the result that the temperature of theLED chips still increases. Accordingly, the amount of light emitted bythe LED chips decreases, variation in wavelength occurs, and thereliability of the LED chips decreases, thus resulting in a reducedlifespan.

Furthermore, it is required to use a substrate to provide the circuitpatterns connected to each LED chip. This increases the price of thebacklight unit as well as the total thickness thereof.

Furthermore, the heating pad is made of a high polymer material havingappearance characteristics similar to those of a thin rubber plate. Thisnot only increases the price of the backlight unit and but also requiresclose attention to be paid to an assembly process.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind theabove problems occurring in the prior art, and an object of the presentinvention is to provide a backlight unit, in which light source modules,that is, LED packages, are directly mounted on a chassis without the useof a PCB, thus reducing the thermal resistance and thickness thereofand, at the same time, decreasing the price thereof.

In order to accomplish the above object, the present invention providesa LED backlight unit without a PCB, including a chassis; an insulatingresin layer formed on the chassis; circuit patterns formed on theinsulating resin layer; and one or more light source modules mounted onthe insulating resin layer and electrically connected to the circuitpatterns.

According to an preferred embodiment of the present invention, theinsulating resin layer has a thickness of 200 μm or less.

Furthermore, the insulating resin layer is formed by laminating solidfilm insulating resin on the chassis or by applying liquid insulatingresin to the chassis using a molding method employing spin coating orblade coating.

Furthermore, the circuit patterns are formed by filling the engravedcircuit patterns of the insulating resin layer with metal material. Inthis case, the engraved circuit patterns are formed by pressing theinsulation resin layer using a stamp having embossed circuit patterns.

Furthermore, the light source modules are LED packages.

In addition, the present invention provides a method of manufacturing anLED backlight unit without a PCB, including the steps of forming aninsulating resin layer on a chassis; forming engraved circuit patternsby engraving circuit patterns on the insulating resin layer; filling theengraved circuit patterns with metal material or plating the engravedcircuit patterns with metal material; forming circuit patterns byremoving metal material that does not fill the engraved circuitpatterns; and mounting one or more light source modules on theinsulating resin layer and electrically connecting corresponding lightsource modules with the circuit patterns.

According to a preferred embodiment of the present invention, theinsulating resin layer has a thickness of 200 μm or less at the step offorming the insulating resin layer on the chassis.

Furthermore, the step of forming the insulating resin layer on thechassis is performed by laminating insulating resin on the chassis insolid film form or applying insulating resin to the chassis in liquidform. In this case, the insulating resin is applied to the chassis inliquid form using a molding method employing spin coating or bladecoating.

Furthermore, the light source modules are LED packages.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic sectional view of an LED backlight unit without aPCB according to a preferred embodiment of the present invention;

FIG. 2 is a flowchart illustrating a method of manufacturing thebacklight unit of FIG. 1;

FIGS. 3A to 3F are schematic sectional views illustrating the respectivesteps of the flowchart of FIG. 2; and

FIG. 4 is a schematic sectional view of a conventional LED backlightunit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An LED backlight unit without a PCB and a method of manufacturing thesame according to a preferred embodiment of the present invention aredescribed in detail with reference to the accompanying drawings below.

As shown in FIG. 1, the backlight unit 100 of the present embodimentincludes a chassis 110. An insulating resin layer 130 is formed on thechassis 110, and a plurality of LED packages 150 is mounted on theinsulating resin layer 130.

The chassis 110 is an element that is used as a casing for the backlightunit 100, and is made of metal material, such as aluminum or copper,which has very excellent thermal conductivity. In particular, it ispreferred that the chassis be made of aluminum material so as to reducethe weight thereof.

The insulating resin layer 130 is made of a high polymer material havingappearance characteristics similar to a thin rubber plate, that is, amaterial similar or identical to a conventional heating pad. For thispurpose, solid film-type insulating resin, having adhesiveness, orliquid insulating resin may be applied to the top surface of the chassis110.

In this case, the solid film-type insulating resin is applied to thechassis 110 using a lamination method, and the liquid insulating resinis applied to the chassis 110 using a molding method employing spincoating or blade coating.

Furthermore, metal material, such as copper, is applied to theinsulating resin 130, or the plated circuit pattern 140 is formedthereon. The circuit pattern 140 is formed by filling engraved patternswith metal material. Unlike a conventional technology, which uses a PCBto form the circuit pattern 140, the present invention directly formsthe circuit pattern 140 on the chassis 110 as described above, thusreducing the total thickness of the backlight unit and, at the sametime, greatly reducing the thermal resistance.

Although not shown, the LED packages 150 include a plurality of sets ofLED packages for emitting red light, green right, and blue light. Theplurality of sets of LED packages are mounted on the chassis 110 inaccordance with a design. Since the LED packages have the same elementsbut emits respective light beams having different colors, only a singleLED package 150 is shown in FIG. 1, for ease of description, and thedescription is made based on this.

Each of the LED packages 150 includes an LED chip 151, LED electrodes152 and 153, a plastic molding casing 154, and a lens 155.

The LED chip 151 is a means for emitting red, green or blue light, isdirectly mounted on one LED electrode 152, and is electrically connectedwith another LED electrode 153 through wire bonding.

Furthermore, the LED electrode 152 is mounted on the positive one of thecircuit patterns 141 and 142 formed on the chassis 110, and the LEDelectrode 153 is mounted on the negative one of the circuit patterns 141and 142.

Furthermore, the LED chip 151 and the LED electrodes 152 and 153 areprotected from the environment by the plastic molding casing 154, andthe casing 154 is covered with the epoxy resin transparent lens 155.

The backlight unit 100 of FIG. 1 is manufactured through the steps ofthe flowchart of FIG. 2, and the respective steps are schematicallyillustrated in FIGS. 3A to 3F to promote an understanding of the presentinvention.

First, at step S110, the insulating resin layer 130 is formed on thechassis 110 to have a thickness of about 10 μm, as shown in FIG. 3A. Theinsulating resin layer 130 is made of a high polymer material havingappearance characteristics similar to a thin rubber plate, that is, amaterial similar or identical to a conventional heating pad. For thispurpose, solid film-type insulating resin, having adhesiveness, orliquid insulating resin may be applied to the top surface of theinsulating resin layer 130.

In this case, the solid film-type insulating resin is applied to thechassis 110 using a lamination method, and the liquid insulating resinis applied to the chassis 110 using a molding method employing spincoating or blade coating. Furthermore, when the liquid insulating resinlayer 130 is formed, the process proceeds to the next step after theliquid insulating resin layer 130 is placed in semi-cured status due tothe evaporation of the solvent thereof.

Thereafter, at step S120, engraved circuit patterns 131 and 132 areformed by engraving circuit patterns on the insulating resin layer 130(which is placed in semi-cured status) using a stamp 120, as shown inFIGS. 3B and 3C. Embossed circuit patterns are formed on the lowersurface of the stamp 120. The engraved circuit patterns are 131 and 132are formed by pressing the stamp 120 onto the insulating resin layer 130using a predetermined force.

Thereafter, at step S130, the insulating resin layer 130, in which theengraved circuit patterns 131 and 132 are formed, is filled with metalmaterial, such as copper, or is plated with the metal material, as shownin FIG. 3D.

Thereafter, at step S140, circuit patterns 141 and 142 are formed byremoving metal material, such as copper, that does not fill the engravedpatterns 131 and 132 or has not been used to plate the engraved patterns131 and 132, as shown in FIG. 3E. In this case, a process of flatteninga coating layer or a plating layer to remove the metal material may beperformed using a physical or chemical method.

Finally, at step S150, the light source modules, that is, the LEDpackage 150, are mounted on the chassis 110 and are electricallyconnected with the circuit patterns 141 and 142, as shown in FIG. 3F. Ingreater detail, the light source modules are mounted on the insulatingresin layer 130 disposed on the chassis 110.

Unlike the conventional backlight unit, the backlight unit 100 of thepresent embodiment does not require any separate PCB or heating pad,thus greatly reducing the thickness thereof. That is, the conventionalPCB, having a thickness of about 0.8 mm, and the conventional heatingpad, having a thickness of about 0.2 mm can be replaced with theinsulating resin 130 having a thickness of 10 μm, therefore a reductionto about 1/100 of an original thickness can be achieved.

Although, in the present embodiment, the backlight unit 100 is formedusing the insulating resin 130 having a thickness of 10 μm, thethickness may be varied within the range of 1 μm˜200 μm in various waysaccording to the design of the circuit patterns. The thermal resistancevalues of the backlight unit 100 depending on variation in the thicknessof the insulating resin layer 130, as determined throughexperimentation, are listed in the following Table 1.

TABLE 1 Thickness of insulating Thermal resistance resin (μm) (° C./W) 10.08 2 0.16 3 0.24 4 0.32 5 0.40 6 0.48 7 0.56 8 0.63 9 0.71 10 0.79 201.59 30 2.38 40 3.17 50 3.97 60 4.76 70 5.56 80 6.35 90 7.14 100 7.94200 15.87

From Table 1, it can be seen that the thickness of the insulating resinlayer 130 that can be applied to the present invention does not exceed0.2 mm (200 μm), which is the thickness of a conventional heating pad.As a result, a reduction in the thickness of the conventional PCB havinga thickness of 0.8 mm can be achieved even though the insulating resinlayer is formed to have the maximum thickness. That is, the totalthickness can be reduced to at least ⅕.

Furthermore, when the thickness of the insulating resin layer is 10 μmas in the present embodiment, the thermal resistance thereof is 0.79°C./W, therefore the thermal resistance of the present embodiment can begreatly reduced, to about 1/87.8 of the original thickness for acomparable conventional thermal resistance of 69.4° C./W, which isachieved by using a PCB having a thickness of 0.8 mm and a heating padhaving a thickness of 0.2 mm. Furthermore, even when the thickness ofthe insulating resin layer is 100 μm, the thermal resistance can bereduced to about 1/8.7 of the original thickness. Furthermore, even whenthe thickness of the insulation resin layer is 200 μm, the thermalresistance can be reduced to about 1/4.4 of the original thickness.

In accordance to the LED backlight unit and the method of manufacturingthe LED backlight unit according to the present invention, circuitpatterns are formed in the insulating resin layer formed on the chassis,so that no PCB and heating pad are required, therefore the totalthickness can be greatly reduced and, at the same time, the totalthermal resistance can be reduced.

Furthermore, no heating pad is required to connect a PCB to the chassis,so that the manufacturing process of the backlight can be simplifiedand, at the same time, the manufacturing cost thereof can be reduced.

Furthermore, a plurality of interfaces generated when the PCB and theheating pad are used can be removed, therefore the thermal resistanceattributable to the interfaces can be additionally reduced.

Furthermore, the thermal resistance is greatly reduced, so that heatgenerated by the LED chips can be smoothly removed, therefore anincrease in the temperature of LED chips is prevented and, thus, areduction in the amount of light and variation in wavelength of the LEDchips is removed. As a result, reliability can be increased and thelifespan of the LED chips can be increased.

Although the preferred embodiment of the present invention has beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. A Light Emitting Diode (LED) backlight unit without a Printed CircuitBoard (PCB), comprising: a chassis; an insulating resin layer formed onthe chassis; circuit patterns formed on the insulating resin layer; andone or more light source modules mounted on the insulating resin layerand electrically connected to the circuit patterns.
 2. The LED backlightunit as set forth in claim 1, wherein the insulating resin layer has athickness of 200 μm or less.
 3. The LED backlight unit as set forth inclaim 1, wherein the insulating resin layer is formed by laminatingsolid film insulating resin on the chassis or by applying liquidinsulating resin to the chassis using a molding method employing spincoating or blade coating.
 4. The LED backlight unit as set forth inclaim 1, wherein the circuit patterns are formed by filling engravedcircuit patterns of the insulating resin layer with metal material. 5.The LED backlight unit as set forth in claim 4, wherein the engravedcircuit patterns are formed by pressing the insulation resin layer usinga stamp having embossed circuit patterns.
 6. The LED backlight unit asset forth in claim 1, wherein the light source modules are LED packages.7. A method of manufacturing an LED backlight unit without a PCB,comprising the steps of: forming an insulating resin layer on a chassis;forming engraved circuit patterns by engraving circuit patterns on theinsulating resin layer; filling the engraved circuit patterns with metalmaterial or plating the engraved circuit patterns with metal material;forming circuit patterns by removing metal material that does not fillthe engraved circuit patterns; and mounting one or more light sourcemodules on the insulating resin layer and electrically connectingcorresponding light source modules with the circuit patterns.
 8. Themethod as set forth in claim 7, wherein, at the step of forming theinsulating resin layer on the chassis, the insulating resin layer has athickness of 200 μm or less.
 9. The method as set forth in claim 7,wherein the step of forming the insulating resin layer on the chassis isperformed by laminating insulating resin on the chassis in solid filmform or applying insulating resin to the chassis in liquid form.
 10. Themethod as set forth in claim 9, wherein the insulating resin is appliedto the chassis in liquid form using a molding method employing spincoating or blade coating.
 11. The method as set forth in claim 7,wherein the light source modules are LED packages.